AN ANALYSIS OF SOLAR P-MODE FREQUENCIES EXTRACTED FROM BISON DATA - 1991-1996

We present a comprehensive frequency analysis of Doppler velocity obse rvations of the visible solar disc made by the Birmingham Solar Oscill ations Network (BiSON) from 1990-1996, i.e. covering the falling phase of activity cycle 22, up to and including the cycle 22/23 boundary. W e have fitted low-degree (low-l) solar p modes in a variety of power s pectra of differing lengths generated from these data. The analysis of the extracted frequencies reveals the expected clear solar-cycle depe ndence; in addition, there is now sufficient accuracy in the data to s how that the low-l modal eigenfrequencies are less affected by the sol ar cycle than their higher l counterparts. The observed low-degree fre quency shifts up to approximate to 3900 mu Hz are consistent - at the level of precision of the data - with an inverse mode-mass scaling. At frequencies above this, the blending of modes adjacent in frequency s pace makes it increasingly difficult to extract reliable frequency est imates. However, our data show indications of a turnover and possibly also an eventual sign change in the solar cycle shifts at frequencies above;approximate to 4000 mu Hz, as seen in higher l data. We have par ametrized the observed shifts as a function of the 10.7-cm radio flux, and produced an activity-corrected, average frequency table which inc orporates eigenfrequencies from 18 4-month and 9 8-month spectra. We a lso present the fitted frequencies from a 32-month power spectrum, gen erated from data collected at or close to solar minimum. In addition, we also searched for frequency asymmetries in the l = 2 mode multiplet s. These could result from strong near-surface magnetic activity, or a buried magnetic field. Our fits merely place an upper limit to any me an asymmetry - over the range 10 less than or equal to n less than or equal to 21 - of between approximate to - 80 and approximate to 170 nH z (3 sigma).